The decision-making process on adjuvant treatment for patients with estrogen receptor positive and human epidermal growth factor receptor 2-negative (ER+/HER2-) early breast cancer may prove challenging. Clinicians should estimate the individual risk of recurrence and weigh the predicted benefit of adjuvant therapies against their short- and long-term toxicities in order to avoid both over- and undertreatment. The careful assessment of the classical clinicopathologic variables is essential to estimate the risk of disease recurrence but is little informative for prediction of chemotherapy benefit for individual patients (1).

The increasing understanding of breast cancer biology has led to the development of multigene signatures that provide prognostic information independent of that provided by standard clinicopathologic features and may help clinicians to better identify those patients with low-risk disease who can be safely spared the toxic effects of chemotherapy (2). All the commercially available signatures have been robustly clinically validated (3) and a plethora of studies consistently showed that their use can lead to a decrease of chemotherapy recommendation in up to 50% of cases (4–10). Accordingly, major Guidelines recommend the use of multigene signatures as a tool to tailor adjuvant chemotherapy decision (11, 12).

Based on this striking evidence, in July 2019 Lombardy was the first Region in Italy to reimburse genomic testing for patients with ER+/HER2- early breast cancer (13). The indication for regional reimbursement was for patients with formal recommendation to adjuvant chemotherapy after multidisciplinary discussion. In April 2022, a group of investigators from six referral Cancer Centers in Lombardy convened to debate the use of multigene signatures in clinical practice and shared their own experience with the tests after reimbursement. This latter point will be reported elsewhere. Here, we reviewed evidence from the literature about the four multigene assays available in Italy and discussed about their optimal use and potential implementation in the evolving field of adjuvant treatment of ER+/HER2- breast cancer.

Several multigene assays have been developed over the past two decades to guide adjuvant therapy decisions. Among them, Oncotype DX, MammaPrint, EndoPredict and Prosigna are the tests currently available in Italy ( Table 1 ).

Modern breast cancer management has become increasingly complex and requires dedicated breast cancer specialists working together to deliver high-quality care throughout the patient journey. The multidisciplinary team (MDT) -defined by the UK Department of Health as a ‘‘group of people of different health care disciplines, which meets together at a given time to discuss a given patient and who are each able to contribute independently to the diagnostic and treatment decisions about the patient’’ (25)- is fundamental in breast cancer management and represents a benchmark for accreditation and funding (26). Different benefits have been associated to MDT-based management: higher patient satisfaction, closer adherence to evidence-based guidelines and, more importantly, better patients’ outcome (27–29). In the context of genomic assays, the fundamental role of the MDT is to identify patients eligible for the test. Accordingly, the prescription of the test usually occurs after MDT discussion of a given patient who underwent surgery and whose histological report is available at the time of the meeting.

However, this process sometimes might lead to different indications for genomic testing by different MDTs on one side, and to a delay in the initiation of the adjuvant systemic therapy beyond the 3-6 weeks recommended by Guidelines (12) one the other side. This latter point might be of particular relevance when MDT decides to order a test to be performed in a central lab.

In this view, we advocated alternative paths for genomic test prescription in an effort to standardize practice and reduce delays to adjuvant chemotherapy initiation. We endorsed the “Oncotype DX reflex testing”, that is the automated preparation and shipping of tumor sample by the pathologist at the time of the histological examination (therefore, earlier the MDT discussion) in cases that meet pre-defined criteria. The implementation of Oncotype DX reflex testing in clinical practice has been shown to improve the timeliness to chemotherapy initiation (30), with potential positive implications in patient satisfaction and outcome.

We endorse the reflex testing for postmenopausal patients < 70 years with ER+/HER2- breast cancers, both node-negative and 1-3 node positive and the following tumor characteristics: T1c-2, Grade 2-3 and at least one of Ki67 21-40% or PgR < 20%. We acknowledge that advanced age, by itself, should not be a criterion to preclude a patient from receiving the most appropriate anticancer treatment and that ‘functional’ rather than chronological age should be considered in the decision making about adjuvant therapy. However, older patients require a more careful evaluation of the risk-benefit ratio of any medical intervention, including a geriatric assessment and a careful consideration of life expectancy and competing risks of mortality that should be performed by the various members of the MDT (31).

No, it doesn’t. Ki67 is a quantitative measure of proliferation and, along with routine IHC measurements of ER, PgR and grade, is useful to classify ER+/HER2- breast cancers with the surrogate definitions of ‘luminal A-like’ (strong ER/PR expression, lower Ki67, lower grade) or ‘luminal B-like’ (lower levels of ER/PR expression, higher Ki67, higher grade) (32). However, while hormone receptor and tumor grade assessment are largely standardized, there is persistent controversy on the optimal thresholds to define “low” and “high” Ki67 values. According to the International Ki67 in Breast Cancer Working Group recommendations, a full agreement on defining a case as “low” or “high” Ki67 exists only for values of 5% or less or 30% or greater, respectively, and these thresholds could be used to withhold or proceed with chemotherapy (33). However, since most ER+/HER2- tumors fall between these two extremes (34), these cutoffs are often of limited clinical applicability. In our and other experience (10, 35), a substantial proportion of tumors with Ki67 > 30% has a low RS and therefore a recommendation of adjuvant chemotherapy for these patients based solely on high Ki67 values would have been questionable. Recent analyses from the TransATAC study showed that Oncotype DX is substantially an estrogen-driven signature, since the correlation between RS and its proliferation module is much weaker than the strong negative correlation between RS and its estrogen module (36). Therefore, it should not surprise if high RS values have been found also in tumors with low Ki67 levels and this has led to a change in recommendation from endocrine therapy to chemo-endocrine therapy (10, 37). Indeed, convincing evidence of the predictive value of Ki67 for chemotherapy benefit is still lacking (38). Accordingly, ASCO Guidelines recommend that Ki67 should be used only as a prognostic biomarker to define individual risk of recurrence (11) and a large fraction of the 2021 St Gallen Panelist believes that a Ki67 threshold for recommending chemotherapy in ER+/HER2- breast cancer is simply not known (32). We acknowledge that Ki67 assessment is an easy and inexpensive method to evaluate tumor cell proliferation that remains extremely useful in many regions of the world with limited access to genomic assays. Nevertheless, we suggest that, if available, genomic assays be employed in those tumors where uncertainty on the benefit from adjuvant chemotherapy still remains despite Ki67 levels.

Age at diagnosis is an important prognostic factor in ER+/HER2- early breast cancer (39) and studies suggested that, among the luminal subtype, tumors arising in young women may be a biologically distinct disease (40). Nevertheless, the role of age and menopausal status has been quite neglected in the development of multigene signatures and the data from validation studies should therefore be interpreted keeping in mind this caveat.

Concerning Oncotype DX, both TAILORx and RxPONDER have found significant interaction for outcome between chemotherapy effect and age or menopausal status (20, 21). In TAILORx, subgroup analysis of women ≤ 50 years old with an RS of 16–25 showed lower rates of distant recurrence with chemo-endocrine therapy compared with endocrine therapy alone. Specifically, women with an RS of 16-20 and high clinical risk (as per MINDACT categorization) and women with an RS of 21-25 irrespective of clinical risk had an absolute reduction in the rate of distant recurrence of approximately 6.5% at 9 years associated with adjuvant chemotherapy (20, 41). Interestingly, this chemotherapy benefit in young women was almost confined to premenopausal women between 46 and 50 years old and waned at younger and older ages and with menopause, suggesting that the benefit is likely due to chemotherapy-induced ovarian function suppression (41). RxPONDER results further corroborate this hypothesis. In that trial, premenopausal women with 1-3 positive lymph-nodes and an RS of 0-25 had a statistically significant and clinically meaningful 40% risk reduction of an IDFS event with chemo-endocrine therapy compared to endocrine therapy alone (5-year IDFS 93.9% vs 89.0%; HR 0.60; 95% CI, 0.43 to 0.83; P=0.002), while postmenopausal women derived no benefit from chemotherapy (5-year IDFS 91.3% vs 91.9%; HR 1.02; 95% CI, 0.82 to 1.26; P=0.89) (21). Somehow consistently with the hypothesis that the benefit of chemotherapy might be primarily driven by its endocrine effect of ovarian function suppression, in premenopausal women who were 50 years of age or older (women who are likely to reach menopause early, with or without chemotherapy), no benefit was observed (21). Similarly to TAILORx and RxPONDER, the updated results of the MINDACT trial showed that patients ≤ 50 years of age derived a significant 5.0% benefit in distant metastasis-free survival (DMFS) with chemo-endocrine therapy compared to endocrine therapy alone (8-year DMFS 93.6% vs 88.6%; HR 0.54; 95% CI, 0.30 to 0.98), while no benefit was observed in older patients (8-year DMFS 90.2% vs 90.0%; HR 0.82; 95% CI, 0.55 to 1.24) (23). It is noteworthy that the chemotherapy benefit in MINDACT was not observed at an earlier follow-up (22), and this indirectly suggests that the benefit is unlikely to be due to a greater cytotoxic effect of chemotherapy in young women, which is known to occur in the first few years after administration (42). Unfortunately, none of these trials was designed to answer the question whether chemotherapy can be replaced by ovarian function suppression in premenopausal women. In all trials, the rate of ovarian function suppression in the endocrine therapy alone arms was limited, and the treatment-induced ovarian suppression in the chemotherapy arms has generated a sort of imbalance in the type of endocrine modulation between arms that hampers the full applicability of the results in current clinical practice, where ovarian function suppression is often planned as a part of endocrine therapy. A definitive answer to this question would require a large adjuvant trial (such as the planned NRG Oncology’s BR009) fully dedicated to premenopausal patients with low genomic risk tumors and investigating whether chemotherapy added to an optimal endocrine therapy provides any benefit. Despite one might speculate that the biological peculiarities of tumors arising in young women (40) could determine a greater cytotoxic effect of chemotherapy, data from TAILORx (20, 41), RxPONDER (21) and MINDACT (23), together with other evidence from prospective trials (43, 44), support the hypothesis that most of the benefit observed with chemotherapy in young women might be due to its endocrine effect of ovarian suppression.

Although Guidelines recommend that genomic testing in premenopausal women with 1-3 positive lymph-nodes should not be offered to guide decisions for adjuvant therapy (11) and some clinicians have interpreted this recommendation as an indication for chemotherapy in all cases, we believe that Oncotype DX may be informative also in these cases and that low genomic risk patients may be considered for either chemotherapy or ovarian suppression based on a comprehensive risk assessment that includes also RS values. Nevertheless, young patients should be informed about the uncertainties in interpreting genomic test results and actively involved in the decision-making process on their optimal adjuvant therapy.

We reviewed relevant data about the role of multigene assays in tailoring the decision-making for adjuvant chemotherapy for patients with ER+/HER2- early breast cancer and provided our viewpoint on specific topics regarding the optimal use of these assays in clinical practice. Nevertheless, the treatment landscape of ER+/HER2- early breast cancer is evolving and novel questions about the potential additional applications of multigene assays are emerging.

The increasing understanding of breast cancer biology has provided the basis for the development of multigene assays aimed to improve our capability of patients’ prognostication and risk stratification. Incorporating these tools in clinical practice has profoundly changed the decision-making for adjuvant chemotherapy for patients with ER+/HER2- early breast cancer and the results from large prospective adjuvant trials have strengthened the clinical utility of multigene assays in this setting. As the treatment landscape of early breast cancer broadens, novel questions arise and new areas of research emerge. In this evolving scenario, the contribution of multigene assays to personalized medicine may become even more important.

The original contributions presented in the study are included in the article/supplementary material. Further inquiries can be directed to the corresponding author.

All authors listed have made a substantial, direct, and intellectual contribution to the work and approved it for publication.